The new Series FPV Plastic flap check valves, from Dwyer Instruments Inc., are suitable where backflow could potentially cause damage to pumps, filters, or process equipment. The valves operate without the need for any adjustments or settings. Line pressure moves the solid plastic flap off the elastomer seat, opening the valve. When the inlet flow stops, back pressure moves the flap back onto the seat, stopping the flow. Because of their all plastic construction, these valves will never jam or stick as a result of rust or corrosion, and they will not contaminate sensitive fluids that come into contact with them. These valves are available in 4in, 6in, and 8in sizes and feature EPDM O-rings and silicone free-construction.